Free-electron coupling to surface polaritons mediated by small scatterers.

The ability of surface polaritons (SPs) to enhance and manipulate light fields down to deep-subwavelength length scales enables applications in optical sensing and nonlinear optics at the nanoscale. However, the wavelength mismatch between light and SPs prevents direct optical excitation of surface-bound modes, thereby limiting the widespread development of SP-based photonics. Free electrons are a natural choice to directly excite strongly confined SPs because they can supply field components of high momentum at designated positions with subnanometer precision.

Toward Complete Optical Coupling to Confined Surface Polaritons.

Optical coupling between propagating light and confined surface polaritons plays a pivotal role in the practical design of nanophotonic devices. However, the coupling efficiency decreases dramatically with the degree of mode confinement due to the mismatch that exists between the light and polariton wavelengths, and despite the intense efforts made to explore different mechanisms proposed to circumvent this problem, the realization of a flexible scheme to efficiently couple light to polaritons remains a challenge. Here, we experimentally demonstrate an efficient coupling of light to surface-plasmon polaritons assisted by engineered dipolar scatterers placed at an optimum distance from the surface.

μeV electron spectromicroscopy using free-space light.

The synergy between free electrons and light has recently been leveraged to reach an impressive degree of simultaneous spatial and spectral resolution, enabling applications in microscopy and quantum optics. However, the required combination of electron optics and light injection into the spectrally narrow modes of arbitrary specimens remains a challenge. Here, we demonstrate microelectronvolt spectral resolution with a sub-nanometer probe of photonic modes with quality factors as high as 10.

Generation and control of localized terahertz fields in photoemitted electron plasmas.

Dense micron-sized electron plasmas, such as those generated upon irradiation of nanostructured metallic surfaces by intense femtosecond laser pulses, constitute a rich playground to study light-matter interactions, many-body phenomena, and out-of-equilibrium charge dynamics. Besides their fundamental interest, laser-induced plasmas hold great potential for the generation of localized terahertz radiation pulses. However, the underlying mechanisms ruling the formation and evolution of such plasmas are not yet well understood.

Ultrafast Electron Microscopy of Nanoscale Charge Dynamics in Semiconductors.

The ultrafast dynamics of charge carriers in solids plays a pivotal role in emerging optoelectronics, photonics, energy harvesting, and quantum technology applications. However, the investigation and direct visualization of such nonequilibrium phenomena remains as a long-standing challenge, owing to the nanometer-femtosecond spatiotemporal scales at which the charge carriers evolve. Here, we propose and demonstrate an interaction mechanism enabling nanoscale imaging of the femtosecond dynamics of charge carriers in solids.

Complete Excitation of Discrete Quantum Systems by Single Free Electrons.

We reveal a wealth of nonlinear and recoil effects in the interaction between individual low-energy electrons (≲100  eV) and samples comprising a discrete number of states. Adopting a quantum theoretical description of combined free-electron and two-level systems, we find a maximum achievable excitation probability of 100%, which requires specific conditions relating to the coupling strength and the transition symmetry, as we illustrate through calculations for dipolar and quadrupolar modes. Strong recoil effects are observed when the kinetic energy of the probe lies close to the transition threshold, although the associated probability remains independent of the electron wave function even when fully accounting for nonlinear interactions with arbitrarily complex multilevel samples.

Role of Symmetry Breaking in Observing Strong Molecule-Cavity Coupling Using Dielectric Microspheres.

The emergence of dielectric open optical cavities has opened a new research avenue in nanophotonics. In particular, dielectric microspheres support a rich set of cavity modes with varying spectral characteristics, making them an ideal platform to study molecule-cavity interactions. The symmetry of the structure plays a critical role in the outcoupling of these modes and, hence, the perceived molecule-cavity coupling strength.

Thermal manipulation of plasmons in atomically thin films.

Nanoscale photothermal effects enable important applications in cancer therapy, imaging and catalysis. These effects also induce substantial changes in the optical response experienced by the probing light, thus suggesting their application in all-optical modulation. Here, we demonstrate the ability of graphene, thin metal films, and graphene/metal hybrid systems to undergo photothermal optical modulation with depths as large as >70% over a wide spectral range extending from the visible to the terahertz frequency domains.

Fundamental Limits to the Coupling between Light and 2D Polaritons by Small Scatterers.

Polaritonic modes in two-dimensional van der Waals materials display short in-plane wavelengths compared with light in free space. As interesting as this may look from both fundamental and applied viewpoints, such large confinement is accompanied by poor in/out optical coupling, which severely limits the application of polaritons in practical devices. Here, we quantify the coupling strength between light and 2D polaritons in both homogeneous and anisotropic films using accurate rigorous analytical methods.

Vancomycin Therapeutic Regime Adjustment in Newborns and Infants with Bacterial Infection: Case Series.

Background: Vancomycin is used mostly to overcome infections caused by methicillinresistant microorganisms. There are no well-established administration protocols for neonates and infants, so the leak of a specific administration regime in that population may lead to serum concentrations beyond the specified range.

Objective: This case series evaluated the pharmacokinetics adjustment from a vancomycin therapeutic regimen prescribed to neonates and infants with bacterial infection at a neonatal public hospital intensive- care-unit, with the primary purpose to verify cases of nephrotoxicity.

Probing the ultimate plasmon confinement limits with a van der Waals heterostructure.

The ability to confine light into tiny spatial dimensions is important for applications such as microscopy, sensing, and nanoscale lasers. Although plasmons offer an appealing avenue to confine light, Landau damping in metals imposes a trade-off between optical field confinement and losses. We show that a graphene-insulator-metal heterostructure can overcome that trade-off, and demonstrate plasmon confinement down to the ultimate limit of the length scale of one atom.